Process of evaporating sulfite waste liquor



June 2, 1959 T. RAMEN 2,888,932

PROCESS 0F EVAPQRATING SULFITE WASTE LIQUOR Filed Sept. 19, 1957 United States Patent PROCESS OF EVAPORATIN G SULFITE WASTE LIQUOR Torsten Ramn, Stockholm, Sweden, assignor, by mesne assignments, to Pedar Limited, New Brunswick, Can- Lada, a corporation of Canada Application September 19, 1957, Serial No. 685,010

(Ilaims priority, application Sweden September 19, 1956 1 Claim. (Cl. 159-47) The present invention relates to a process of evaporating sulfite waste liquor in a multi-stage evaporation installation, in which the waste liquor is initially evaporated in one or more stages operating at relatively low temperatures, preferably under reduced pressure, and is then further evaporated in a number of stages operating at higher temperatures.

In installations of this type it has heretofore been customary to pass the liquor, after partial evaporation in the stages operating at the relatively low temperatures, to a stage operating at an intermediate temperature (e.g. the third evaporation stage in a five-stage evaporation plant) and thereupon to the stage operating at the highest temperature of the plant (the first stage, it being understood that the designation first, second etc. stage refer to the temperature levels of the stages, the first stage being that which has the highest temperature etc.). It has been found, however, that with this manner of op erating incrustations are easily formed in said intermediate stage, requiring frequent cleaning of the heating surfaces of said stage.

The object of the present invention is to eliminate this disadvantage and to carry out the process in such a manner that the troublesome incrustation is inhibited or reduced.

In accordance with this invention it has been found that this object is achieved by passing the liquor from the stages operating at said relatively low temperatures directly to the stage operating at the highest temperature and passing the liquor thereupon to a stage operating at an intermediate temperature.

The invention will be described more in detail with reference to the accompanying drawing, which illustrates diagrammatically an embodiment of an installation for evaporating fermented sulfite waste liquor in accordance with this invention.

Referring to the drawing, the numerals 1, 2, 3, 4 and 5 designate five evaporating apparatus and the numerals 6, 7, 8, 9 and heating bodies associated therewith, the liquor being evaporated in each stage circulating between each evaporator and associated heating body. In the heating bodies the waste liquor is heated by indirect heat exchange with live steam (heating body 6) or with the vapors driven off in each preceding stage (heating bodies 7, 8, 9 and 10) in a well-known manner. In the two highest evaporating stages the liquor circu1ation between each evaporator and associated heating body is preferably forced circulation by means of pumps (not illustrated on the drawing) while in the three lower evaporation stages selfcirculation is preferably utilized.

The numeral 11 designates a condenser in which the vapors driven off in evaporator 5 are condensed. 12 is a condensate collecting tank, in which the alcohol-containing condensate of the vapors driven ofi in evaporator 4 and condensed in the heating body 10 are collected and to which also the alcohol-containing condensate from condenser 11 are conducted. 13, 14 and 15 are condensate collecting tanks for receiving the liquor vapor condensates formed in heating bodies 7, 8 and 9.

The condensate formed in each stage is conducted, as indicated on the drawing, to the condensate collecting tank of the next higher stage to be heated by and mixed With the condensate collected therein. The mixture of all condensates is then further heated in a heat exchanger 16 with live steam and is utilized in heat exchangers 17 and 18 for preheating the liquor. Part of the mixture is recirculated to the tank 15.

As seen from the drawing, the liquor (the flow of which is shown by wide lines) is introduced into evaporator 4, is conducted therefrom to evaporator 5, through heat exchangers 18 and 17 to evaporator 1, therefrom to evaporator 3 and finally to evaporator 2, wherefrom the finally evaporated liquor is withdrawn. In the conduit from the evaporator 1 to the evaporator 3 there may be arranged an expansion vessel 19 in which the pressure of the liquor is lowered to the pressure prevailing in evaporator 3. The vapors formed by this expansion are suitably conducted to heating body 8.

The evaporators may operate at temperatures of e.g. 115, 105, 90, and 55 C., respectively.

The incrustation problems in the evaporation of sulfite waste liquor are caused by the decreasing solubility of calcium sulfate when the temperature is increased. Due to this fact, in the evaporation at a higher temperature and simultaneously increasing concentration, a precipitation of calcium sulfate tends to occur in the stages operating at a higher temperature and may be deposited on the heating surfaces as incrustations. It has particularly been found that if the liquor from the fifth evaporation stage is passed to the third evaporation stage, the incrustations in this stage become very troublesome. This difficulty is avoided according to this invention by passing the liquor directly to the first stage. Because the volume of liquor circulating between the evaporator and its heating body may be kept very great in this stage, the liquor supplied to this stage will be heated practically immediately to the temperature prevailing in this stage, so that practically all precipitation of calcium sulfate occurs directly in the circulating liquor and only an unimportant deposition on the heating surfaces occurs.

I claim:

A method of evaporating sulfite waste liquor in a multistage installation, in which the liquor is first evaporated in at least one stage operating at a relatively low temperature, preferally under reduced pressure, to be subjected to continued evaporation in a number of stages operating at higher temperatures, which comprises passing the liquor from said stage operating at a. relatively low temperature directly to the stage operating at the highest temperature of the installation and passing the liquor therefrom to a stage operating at an intermediate temperature, and passing the liquor from said intermediate temperature stage to a stage operating at a temperature between that of the highest temperature stage and that of said intermediate temperature stage.

References Cited in the file of this patent UNITED STATES PATENTS 2,181,731 Hinckley Nov. 28, 1939 FOREIGN PATENTS 148,692 Sweden Feb. 1, 1955 

